Control method in reactions between hydrocarbons and metal oxides



u y 1952 w. K. LEWIS EI'AL 2$503,608 CONTROL METHOD IN REACTIONS BETWEEN I HYDROCARBONS AND METAL OXIDES Filed Nov. 29, 1950 MAKE GAs OUTLET J QYCLONE YCLONE 25a.

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A 4'':L 3 Z) 5 Am INLET FEED INLET Qfizrrerz I4. baw'zlsr Eda-La Q. GCLLL LOIZd b wwmm Patented July 15, 1952 ES PATENT. OFFICE CONTROL METHOD l'N REACTIONS BE- I TWEEN HYDROCARBONS AND METAL OXIDES Warren K. Lewis, Newton, and Edwin R. Gilliland,

Arlington, Mass., assignors to Standard Oil Development Company, a corporation of Delaware Application November 29, 1950, Serial No. 198,144

12 Claims. (01. 252,373)

1 V The present invention, which is a continuation-in-part of Serial No. 32,704, filed June 12, 1948, now abandoned, is directed to the production of gases containing carbon monoxide and hydrogen by the reaction between a hydrocarbon and a reducible metal oxide, and more particularly, to a control mechanism for this reaction. The reaction between a hydrocarbon and a reducible metal oxide for the production of gases containing carbon monoxide and hydrogen is known. Of the metal oxides which have been proposed for this reaction, one of the few which has'an oxidizing potential such as to direct the conversion of the hydrocarbon gases only to carbon monoxide and hydrogen is zinc oxide. Because of the low distillation temperature of zinc and the difficulty of handling ,zinc vapors, and the low hydrocarbon conversions attainable therewith, this metal oxide does not offer much promise for a commercial operation. This has caused the investigation in this field to be centered on other metal oxides, all of which seem to have oxidi'zing potentialities such that unless the oxidation is carefully controlled, the conversion of the hydrocarbon goes in a large measure to the production. of carbon dioxide and water. As a mat- .ter of fact, it appears that with all these other metal oxides the reaction first goes predominantly to carbon. dioxide and water and the resulting mixtureof unconverted hydrocarbon, carbon dioxide and water undergoes a. reformation in contact with the metal, the oxide of which supplied "the oxygen. Thus, in carrying out this process with all metal oxides except zinc oxide and the "like, thefmake gas contains carbon dioxide and water. and some unconverted hydrocarbon.

1 .It has been proposed to practice this process by utilizing the so-called fluidized solid technique ina continuous process employing two reaction zones, in one of which hydrocarbon continuously contacts a fluidized bed containing metal oxide ,Land-in-the other of which air continuously contacts; a fluidized bed containing free metal and inwhich there is continuous circulation between the two beds.

In thistype of operation the solid contacting agent is in the form of particles, none not which has a size substantially greater than lilq mesh and a large proportion of which have a size between 200 and 400 mesh and some of which may have a much smaller size down to about 5 microns; Best fiuidization is obtained when there ista fairly wide distribution of particle sizes. The contacting gases pass upwardly through a bed jot-such particles ata velocity such as to hold the} particles in suspension in a dense turbulent condition. Ordinarily this velocity will .be between .3 and 5 feet per second, usually. in the lower end of the range, the values given. being superficial velocity of the gas through an empty contacting zone. A particular proposal has been to maintain in the hydrocarbon conversion zone a bed composed, substantially completely, of metal, either as such or supported on a suitable carrier, and to addto this bed, continuously, an amountof metal oxide such as to supply one atom of oxygen for each atom of carbon fed-into the zone. Thistypeof operation has been applied specifically to copper oxide and it has been found that when careful control is exercised, the make gas can becomposed almost entirely of carbon monoxide and hydrogen. Theexperimental evidence clearly indicates that the course of the reaction is such that part of' the hydrocarbon is converted completely to carbon dioxide and water before the remainder of the hydrocarbon is converted. .In this reaction all of oxygen supplied by the metal oxide is consumed and the residual hydrocarbon reacts with the carbon dioxide and water inthe presence of the copper to yield carbon monoxide In order to produce continuously a make gas" of fairly-uniform composition, according to the procedure outlined above, continuous control must be exercised on the feed rates of the hydrocarbon and metal oxide to the hydrocarbon conversion zone. The operator must beable to tell quickly when his make gas deviates from the desired composition so as to be able to make quickly, the necessary adjustments to maintain the composition of the -make gas uniform. Thus, the desired conversion product may be a gas containing two mols of hydrogen per mol of carbon monoxide, if the gas is to be employed, say,'for the hydrocarbon synthesis reaction; or the desired composition may-also-include a gas comprising agreater or smaller fixeddesired amount of carbon dioxide in accordance -.with the purpose for which the gas is'to be employed. 'In otherwords, .the operator must-be able'to' ascertain if he is feeding to the hydrocarbon conversion-'zonethe proper ratio of oxygen ;as metal oxide'to carbon as methane to obtain the gas of desired composition and he must also always beable to ascertain if the reforming reaction is going to completion or. if not, whether he is maintaining a. desired conversion level within the reactor, that is, if he wishes to obtain a'gas having any desired carbon dioxide content. Thus, the operator may be feeding the proper proportion of metal oxide and 3 methane but the reforming activity of the contact mixture in the hydrocarbon conversion zone may fall below the desired conversion level, so that the composition of the make gas suffers.

Ordinarily, in' order properly to operate the reforming reaction taking place in a conversion zone, a complete analysis of the off-gas would be required. This gas customarily contains five components, namely, hydrogen, carbon monoxide, carbon dioxide, unreacted methane and,

the operation of the aforesaid type is readily efiected'by making a few simple determinations on the make gas, in place of a complete timeconsuming analysis. For complete control, the operator must first determine the carbon dioxide content of the make gas. Then, according to the present invention, the operator subjects a small quantity of the make gas to a reformation operation'in which is utilized a highly active catalyst at a temperature sufficiently high to secure completion of thereforming reaction. The operator then determines the carbon dioxide content of the product of this reforming reaction. In order tomake possible control of this type it is necessary to feed to the reactor an amount of oxygen as oxide, slightly in excess of at least the stoichiometric equivalent of the In other carbon to produce carbon monoxide. words, it is necessary to insure that the "make gas will'always contain some carbon dioxide.

Thus, the control method does not provide for "maintenance of precise stoichiometrical quantities of one to one atomic ratio of oxygen and carbon in the feed to the hydrocarbon conversion zone but for the maintenance of the slight excessof oxygen within those'proportions which may be tolerated.

'If,'in the practice of the control method of the present invention, the carbon dioxide'content of'the make gas exceeds a predetermined quantity; the operator knows that he is feeding an excess of oxygen as oxide over the predetermined amount to the hydrocarbon conversion 1 zone, or'that the reforming reaction in theconversion zone is not going to completion. Then,

if the oif gas from the pilot reforming operation. contains an amount of carbon dioxide in excess of that predetermined for satisfactory operation, he knows that heis feeding toomuch oxygen to the hydrocarbon'conversion zone and can' either' reduce the oxygen feed orincrease the hydrocarbon'feed" correspondingly. I On the other hand, if the product gasfromthe pilot reforming operation contains anamount of carbon'dioxide'predetermined for satisfactory operation he knows that, the carbon dioxide con- 7 tent of the make gas being excessive, the reforming operation in the hydrocarbon conversion zone is not going to completion. This can be compensated for in the ordinary case by increasing the temperature in the hydrocarbon conversion zone or increasing the residence time of the reactants by slowing down the gas velocity in the hydrocarbon conversion zone or increasmosses ing the amount of solids held up in the conversion zone. However, should the operator desire to maintain less than complete conversion of hydrocarbon, the operator is in position to make such minor adjustments so as to maintain a constant difference between the carbon dioxide content of the effluent from the pilot unit and that from the analytical unit. Therefore, if the operator was-getting a 100% conversion in the main reactor, then the composition of thef'make gas would be identical with the composition of the pilot unit product gas.

Several types of devices for quickly determining the carbon dioxide content of a gas are known and any of these may be employed in the practice of the present invention. For example, the infrared ray spectrometer quickly and accurately gives a measure of very minute amounts of carbon dioxide in gas; also, a conventional pH meter may be employed for this purpose, utilizing water as the medium in which the hydrogen electrode'is immersed and passing the gas to be examined through the water. These and other types of indicators indicate'the car'- bon dioxide content of the gas as an electrical quantity. This electrical quantity maybe utilized to actuate valves controlling the feed of metal oxide or hydrocarbon or both to the hydrocarbon conversion zone. These specific control arrangements constitute no part of the present invention since, for the purpose of the present invention, the operator, having made the: determinations which constitute the real control method of the present invention, can manipulate the feeds of the hydrocarbon and the metal oxide manually.

In the pilot reforming operation of the present invention there is employed a highly. active catalyst such as nickel-alumina catalysts prepared by co-precipitation ofthe nickel oxide-and alumina, or even a'copper-silica gel catalyst which may likewise be prepared by a co precipitation method or by impregnation of silica gel with a copper salt solution, followed by the usual drying, roasting and. reducing steps. These catalysts are highly effective catalysts in this reforming operation, even at temperatures as low as 1600" F. In order, however, to insure completion of this reaction, this pilot reforming unit is operated at a temperature between 2000- and 2400 F.

By way of explanation, it may be pointed out that if, in those cases. where it is desired to produce a mixture of carbon monoxide and hydrogen, e. g., to be used in the hydrocarbon synthesis process, the feeds of oxygen and: carbon to the main process were in exactly stoichiometrical amounts for the production of carbon monoxide and hydrogen the gas produced in the pilot reforming step would contain only traces'of carbon dioxide, regardless of what 'happened'in the main' process. If the oxygen fed to the main process were supplied in excess of the'amount necessary to convert the carbon fed to carbon monoxide, the products of the-pilot reforming operation would contain a small amount of carbon dioxides which can be determined bycalculation, regardless of what happened in the main process. Therefore, in' accordance with one embodiment of the present invention, control 'of the process is predicated on maintaining a content of carbon dioxide in the product gas of the pilot reforming operation between fixed relatively narrow limits, asfor example, between. and 2% or perhaps between 1 and 3%. These limits synthesis feed gas.

'poses l are desirable when the product gas is to be used in the synthesis of hydrocarbons from carbon monoxide and hydrogen formed in the reformer and in which process it is customary not to employ excessive quantities of carbon dioxide in the However, should it be desired to employ the gas for other purposes, which purmay envisage-the presence of a gas containing larger quantities of CO2, the efiluent from the pilot reactor need not be restricted to a C02 limit of 3%, but may be as high as 12-15% in some gases.

If the carbon dioxide content of the gas from the pilot unit falls below the fixed minimum, the operator knows that his feed of oxygen to the hydrocarbon conversion. step is deficient- On the other hand, if the carbon dioxide content of this gas exceeds the fixed maximum, the operator knows that his oxygen feed to the hydrocarbon conversion step is excessive. It is to be emphasized, however, that knowledge of this one fact is not adequate to insure proper control of the main process for the production of the desired make gas." In addition the operator has to know the carbon dioxide content of the "make gas" itself.

The nature of the present invention may be more fully understood from the following detailed description of the accompanying drawing in actor I is an overflow pipe 6 which is connected to the constricted portion of reactor 2. In like manner, an overflow pipe I connects the expanded portion '5 of reactor 2 with the restricted portion tothe reactor I. This pipe is provided with a slide valve or with another feed .control element 8.

.A feed line 9 for hydrocarbon gas is provided below the constricted portion 3 of reactor I.

This feed line is preferably arranged so as to pick up finely divided solid leaving the lower end of pipe I and carry it up into reactor I. In like .manner, there is provided below the constricted portion 3 of reactor 2, a feed line II for air, arranged to pick up finely divided solid leaving the lower end of overflow pipe 6 and carry it up through reactor 2. A suflicient quantity of solids is maintained in the system so that when it is in operation finely divided solids are continuously overflowing from each reactor into the other.

Residual air leaves the top of 2 through line I2 which discharges into a cyclone I3 from the bottom of which separated solid is returned to pipe I through leg I4 and from the top of which residual air leaves the system through line I5. Makegas leaves the top of reactor I through line I6 which discharges into a separator I! from the bottom of which separated solid is returned to pipe 6 through leg l8 and from the top of which "make gas leaves the system through line I9.

Attached to line I9 trolled by a valve 2 I is a branch line 20 con- This line conducts a small portion of the "make gas to an analytical unit I 22 which s a suitable device of the type heretoby manipulation of which a measured amount of "make gas can be fed continuously to a reformation unit 24. This unit is illustrated merely'as a reactor 24 which is loaded with reforming catalysts and is suitably heated by an electrical coil.

fluidized solid technique.

It will be apparent, of course, that this reformingunit may assume many forms. Itmay, for example. be a unit operated according to the The ofi gas from this unit is piped by 1ine'25 to an analytical unit 28 which'will, in the ordinary case, be the same as unit 22 The operating conditions in the main process constitute no part of the present invention. It may be mentioned, however, that the hydrocarbon conversion unit will usually be operated at a temperature between about 1500 F. and 2000" F., depending upon the'metal oxide employed and upon the reforming catalyst employed. When copper oxide is utilized, it is present as a composite with a suitable carrier, silica gel being preferred. The silica gel may carry be tween 3 and 30% of copper, the quantity preferably being in the lower end of the range so as to provide for a greater transport of heat between the metal oxide zone and the hydrocarbon conversion zone. With copper the hydrocarbon conversion is preferably maintained between 1600 F.

and 1850 F. In this operation, when an approximately 2/1 Hz/CO hydrocarbon synthesis gas is being prepared, the feed of copper oxide to the hydrocarbon conversion is regulated so as to be between about and 2% in excess of the stoichiometrical amount to convert the carbon fed to this zone to carbon monoxide.

As has been pointed out, the control method employed in accordance with the present invention is well adapted to utilization in the production of hydrocarbon synthesis gas. In the production of the latter it is preferable to operate in order that the off-gas should have acarbon dioxide content lower than about /2% and generally 3% CO2 should not be exceeded. The CO: content of the gas. however, depends upon the skill of the operator, the analytical control, the type of catalyst, the ratio of the reactants and other variables. Where reaction control is good, 3% CO2 should not have been exceeded.

Instead of preparing synthesis gas in accordance with the process described heretofore, it may be desired to produce a metallurgical reducing gas, the reducing power of which is controlled for the selective reduction of a particular metal oxide, for example, such as the reduction of F6203 to FeaO4 or the reduction of a tin ore containing iron oxide. In the latter case, selective reduction of the tin oxide should be accomplished without reducing the iron oxide to metallic iron. Partial reduction of the iron oxide does not hinder separation of the metallic tin reduced from the tin oxide. This type of reducing gas requires a high CO2 to CO ratio to keep the iron from being reduced too far.- When it is desired to make such a gas, the unit for reformmg the hydrocarbon reducing agent must be operated accordingly. The allowable CO2 to CO ratio in the reducing gas coming into contact if'the tin ore is being reduced at 800 C. it is desirable to keep the CO: to CO ratio above 0.53

to prevent reduction of FeO, while at 600 C.

amar-s ..:7 "the ratio should be above 0:85. It us-ually desirable to operate the ireforming unit, which isgpr'oducing the reducing-gas, for maximum-conversion of'hydrocarbon; 'Where it is-practicable tojrecyclejgas leavingthe'reduction unit back to its intake it becomes desirable to reform" to a low .602 content; and control the. CO2 to COratio El'1'te1'lngjllhe re'ducer'by'the rate of this recycle. "The essential facts underlying this invention, whichmake it possibleto determine the performance of 'a-reforming unitjlcymaking only two analytical dete1-minations,name1y, the iCOi-jcontents ofthe reformed gas onthe one hand' and of the gas from'the pilot reforming unit ron-the other, are two. In the first place, at thet'emperature levels involved thesecatalysts employed 'for -the-"refo'rming reactions are-suchgood catalysts for the Leo-called water gas shift reaction, COz"-|-H2=,GOl-H20 ,fthat the. gases leaving the "'reformer are substantially at equilibrium 'from i the jp'oint of view-of water-gas shift; The con- "stant' of the reaction is well, knownand is, dependent on the-temperature. Consequently, knowing the actual operating temperature of the reforming'u'm't from-which the gas samplecomes, one knows the value'of this constant. It is'true thatthe'reaction may-shift somewhat as the gas sample? is-removedfor {analysis unless the sampling'techniq'ue provides adequately rapid temperature quenching 'Even so, "it is found that. for any reasonable technique ofsample'withdrawal which-providesrapid cooling, the change in the value of theconstant from that corre- "spondingto the temperature of the reformer itself issmall'enough so that a calibration of-the apparatus by the determination-of this modified value of the constantbycomplete analysis of gas samples removed under "normal operating conditions is satisfactory for the carrying out of the invention. Therefore, knowing the value of the constant thus determined corresponding to the actual measured operating temperature of the reforming unit in question and knowing the compositio'njof the hydrocarbons orotheriuel fed to the reformer,- by means of hydrogen and carbon balances, the knowledge of the COz'con- -tent of the gas is enough to enable one to compute the composition of the reformed gas. The second-essential fact is that by operating a reformerwith'an active catalyst, used in sufiicient quantitygat temperatures of 2000 F." and above, the conversion of any hydrocarbon or equivalent material in the feed to water gas is substantially complete.

As a further illustration of'an application of the presentinvention, the following example is given.

Example aireforming operation using substantially pure methane, wherein it is desired to produce approximately a 2/1 Hz/CO gas for hydrocarbon synthesis purposes-the reforming unit is operatedat 1650 F. At-this reformer temperature the calibration of the sampling equipment shows that one obtains a waterf gas shift con'stant'of approximately 0.8. The pilot unit isoperated at 200 0*F:-and at thisfltemperature its calibration -shows-a'constant of 0.48. The CO2 content of the reformer gas is found to be 3.5% on ardry basis and of the-outlet gas-from the'pilot unit. 0.6%. Thisall the iactual-iniormation needed for applying the invention in this case.

From this information "it follows that the product gas from-the pilot unit is"0.6%' CO2,

33.55%2CO andi-65I85.% .Hi .on :a dry baslssgand that on this same basis. it contains 2.45% of water vapor. This .isanatomic ratio of oxygen to carbon 10f "1.09; :Applying this figure .to .the 5 data on the reformer gas, its analysis turns-out ta kie-3.5% CO2,. 29;9.% CO,.58.25% H2 andl8.35%

"methanegtogether :With 8.56% water.; In other -words,'..the methane conversion in the reformer is only 80%.' iTo a'ohieve ithe .-.resu1ts de'sired,fthe opera/ton must take suitable steps to get higher conversion in the primary reformer andshould. if possible, achieve this with a lower. excess'oxygen relative to :metha'ne fed to the reformer as -metal oxide'.

Gnce the 'control :operations are functioning satisfactorily, there; is no need for the operator to go through the details I of computation "given above. For given reforming temperaturearthe CO2:determinationsdisclose immediately whether "the-'ope1-ati0n-is going as it should and,..if"not, what changes must-be made to bring it into line.

The nature and objects of the present. invention having been described and illustrated,'they are not intended-to be limiting in any Way..

'What is claimed is:

1. In a process in which a hydrocarbon-is partially reacted in-a conversion zone wi-th' areadily reducible metal-oxide to produce-oxides of-carbon, hydrogen and water and the resulting mixture containing unreacted' hydrocarbons is subjected to 'a'reforniing operation within'the same conversionzone to producea makegas-comprising I carbon monoxide and hydrogen, the improvemerit-which comprises supplying to said con-version-zoneoxygen-as metal oxide equivalent to at least-morethan-one atom of oxygen for each I atom of carbon added as hydrocarbon, producing a "make gas"- insaid conversion zone containing a minor quantity of carbon dioxide, passing a gas stream comprising a minor portion of said make gasfto a zoneindicating the-carbondioxide content" of' said "gas, subjecting another :portion of said make gas to a reforming operationin a reforming zone controlled-to insure-completereactionvo f any hydrocarbon by carbonidioxide and water contained in said make gas, passingfithe gaseous efiluent from said. last-named zone'to a 'zoneindicating the carbon: dioxide content .of

.saidefliuent and 'controlling'the reaotion'condi- 5O ti'ons 'in said first-named reaction zone, responsive to the'carbon dioxide content of said gas streams,

to .insure the desired methane conversion.

2.? The process of claim 1' wherein the said rates of said initial reactants to said initial reaction 55, zone are controlled responsive to said carbon dioxide content.

:3. "The processlof claim 1 whereinthe temperature in said initial conversion zone. is. controlled responsive to said carbondioxide content.

4."The process according to claim 1 wherein theieed ofmetal' oxide. and hydrocarbon to said initialreaction zoneis controlled so as to maintainythe carbon dioxide content of the product gas from, the reformation of the makev gasfiat least about. e

' 5." Thei processor claim4 whereinis'aid carbon dioxide content .of .the. product gas is between I aboutI /2and'l3%..

"6.,'I'he processaccordingto claim 1 "in which 7 "the amount of oxygen relative to the carbon fed to the reaction zone is controlled so as to beat least about /2% in excess of the stoichiometrical amount. necessary to convert carbon to carbon -monoxide.

I. The process of claim 6 wherein said metal oxide is /2 to 2% in excess of the stoichiometric amount of oxygen.

8. The process according to claim 1 wherein said metal oxide is copper oxide supported on a carrier.

9. The process of claim 8 wherein said carrier is silica gel. 1

10. The process according to claim 1 in which the make gas is reformed by being contacted with copper supported on silica gel at a temperature of between about 2000 and 2400 F.

11. The process of claim 1 wherein said effluent from saidauxiliary reforming zone has a carbon dioxide content in the range of 0.5 to 15%.

12. An improved process for preparing gas adapted to be employed in the hydrocarbon synthesis operation containing substantially 2 mols of hydrogen per mol of carbon monoxide, which comprises passing slightly more than one atom of copper oxide per mol of methane to a catalytic methane reforming zone wherein initially oxides of carbon, hydrogen and water are produced and 10 the resulting mixture is subjected'to a reforming operation with unreacted methane to produce a make gas composed essentially of carbon monoxide and hydrogen and a minor quantity of carbon dioxide, passing said minor portion of said make gas to a zone indicating the carbon dioxide content of said gas; passing another minor'portion of said make gas to a reforming operation in an auxiliary reforming zone controlled to insure complete reaction of unreacted methane with carbon dioxide and water contained in said make gas, passing the gaseous named reaction zone responsive to the carbon I dioxide content of said gas streams.

WARREN K. LEWIS. EDWIN R. GHJLHJAND.

No references cited. 

1. IN A PROCESS IN WHICH A HYDROCARBON IS PARTIALLY REACTED IN A CONVERSION ZONE WITH A READILY REDUCIBLE METAL OXIDE TO PRODUCE OXIDES OF CARBON, HYDROGEN AND WATER AND THE RESULTING MIXTURE CONTAINING UNREACTED HYDROCARBONS IS SUBJECTED TO A REFORMING OPERATION WITHIN THE SAME CONVERSION ZONE TO PRODUCE A "MAKE GAS" COMPRISING CARBON MONOXIDE AND HYDROGEN, THE IMPROVEMENT WHICH COMPRISES SUPPLYING TO SAID CONVERSION ZONE OXYGEN AS METAL OXIDE EQUIVALENT TO AT LEAST MORE THAN ONE ATOM OF OXYGEN FOR EACH ATOM OF CARBON ADDED AS HYDROCARBON, PRODUCING A "MAKE GAS" IN SAID CONVERSION ZONE CONTAINNG A MINOR QUANTITY OF CARBON DIOXIDE, PASSING A GAS SREAM COMPRISING A MINOR PORTION OF SAID "MAKE GAS" TO A ZONE INDICATING THE CARBON DIOXIDE CONTENT OF SAID GAS, SUBJECTING ANOTHER PORTION OF SAID "MAKE GAS" TO A REFORMING OPERATION IN A REFORMING ZONE CONTROLLED TO INSURE COMPLETE REACTION OC ANY HYDROCARBON BY CARBON DIOXIDE AND WATER CONTAINED IN SAID "MAKE GAS", PASSING THE GASEOUS EFFLUENT FROM SAID LAST-NAMED ZONE TO A ZONE INDICATING THE CARBON DIOXIDE CONTENT OF SAID EFFLUENT AND CONTROLLING THE REACTION CONDITIONS IN SAID FIRST-NAMED REACTION ZONE RESPONSIVE TO THE CARBON DIOXIDE CONTENT OF SAID GAS RESPONSIVE TO INSURE THE DESIRED METHANE CONVERSION. 